In the processing of fabrics with liquid ammonia, a web of the fabric is directed into a closed chamber, in which the fabric is contacted by the liquid ammonia. Typically, this may be accomplished by directing the fabric web into a trough containing liquid ammonia and then conveying the fabric under controlled conditions while the fabric remains saturated with the ammonia. The primary treatment chamber is, in such cases, saturated with ammonia vapor.
Because of the poisonous and unpleasant nature of the ammonia vapors, it is desirable to maintain the interior of the treating chamber at a slightly negative pressure relative to the ambient, so that leakage out of the chamber is avoided or minimized. At the same time, it is desirable to avoid leakage into the chamber of excessive atmospheric air. Excessive influx of air can introduce undesirable amounts of moisture, which can interfere significantly with ammonia recovery procedures. Likewise, too much air in the system can be detrimental.
The present invention provides simple yet highly reliable and effective means for sealing the entrance and discharge openings of a liquid ammonia or similar treatment chamber. Importantly, the new sealing arrangement provides for effective sealing of the entry and discharge openings of the chamber without resulting in excessive frictional drag on the fabric being conveyed therethrough. The latter can be an important consideration in the processing of knitted fabrics, for example, where it is desired to carefully limit and control fabric tensions during the processing.
In the pressure seal of the invention, opposite surfaces of the fabric are maintained in sliding contact with effectively stationary surfaces of the seal. On one side, the seal can be formed by a rigid guide member. On the opposite side, the seal is formed by a thin, highly flexible web of low friction material, such as Teflon-impregnated glass fiber cloth. This thin, flexible material is urged lightly against the fabric by a deformable resilient member. The construction of the seal is such as to provide highly effective closure of the chamber while at the same time maintaining frictional drag on the fabric at a practical minimum and also highly uniform across the width of the fabric.
In accordance with one aspect of the invention, the flexible low friction web material is movably mounted, enabling it to be shifted from time to time to bring a new surface area into operative position as may be necessary to compensate for wear.
In a typical processing chamber, the entrance and exit openings may incorporate double seals, with an intervening zone between the interior and exterior of the treatment chamber. In such cases, a pair of sealing assemblies may be utilized in conjunction with a single length of the low friction web material, for convenience and greater simplicity.